1. Field of the Invention
This invention relates to a method for the production of glucose by the use of the transglucosidase produced by genus Bacillus.
2. Prior Art Statement
Enzymes which effect transfer reaction of sugars are of two types, one relying on transferases and theother resorting to the reverse reaction of hydrolases. The transferases are classified by the kind of residue taking part on the transfer reaction into seven types. Among the transferases, those which take part in the transfer reaction of sugars are characterized by using oligosaccharides or polysaccharides as donors and transfer the residues thereof into other suitable acceptors such as monosaccharides, oligosaccharides, and various alcohols. They also include those enzymes which effect transfer of various saccharides such as glucose residues, xylose residues, and galactose residues. Alternatively, the transferases are classified by the kind of the bonding through which the transfer reaction takes place. As concrete examples of the industrial application of transferases, there can be cited the production of cyclodextrins by the use of a cyclodextringlucanotransferase, the production of coupling sugars by the use of the same enzyme, and the production of glucosylstevioside. As examples of the industrial application utilizing the reverse reaction of hydrolases, there can be cited the production of branched cyclodextrins by the use of pullulanase and the production of isomaltose by the use of glucoamylase.
The inventor has found that a certain sugar transferase manifests a conspicuous effect in increasing the yield of glucose in the hydrolysis of starch by the use of a glucoamylase. At present, glucose is produced by first liquefying starch (dextrin) with an .alpha.-amylase and then saccharifying the liquefied start with a glucoamylase.
Since the glucoamylass is capable of hydrolyzing both the .alpha.-1,4-glucosidic and .alpha.-1,6-glucosidic bonds of starch, it can hydrolyze starch substantially completely into glucose when the starch is in the form of a dilute solution. Since in the saccharification carried out on a commercial scale, starch is used in a high concentration of 30 to 35%, the produced glucose succumbs to polymerization induced as by the reverse synthetic action inherent in glucoamylase and, as a result, the yield of glucose generally falls in the range of 93 to 95%. The remainders are maltose, isomaltose, panose, and other oligosaccharides of still higher molecular weight. The idea of effecting further hydrolysis of these remaining oligosaccharides thereby attaining an addition to the yield of glucose has long been desired by the industry in the production of glucose.
In the saccharification of starch with a glucoamylase, it has been known that when the reaction of saccharification is carried out in the presence of a pullulanase possessing an ability to hydrolyze the .alpha.-1,6-glucosidic bond, it is promoted so much as to increase the yield of glucose by 0.5 to 2% (Japanese Patent Publications SHO No. 54(1979)-29570, SHO No. 57(1982)-39, SHO No. 57(1982)-174089, etc.) An increase in the yield of glucose can also be attained by the use of a certain kind of .alpha.-amylase (Japanese Patent Publication SHO No. 61(1986)-19498). Pullulanase in an enzyme capable of hydrolyzing the .alpha.-1,6-glucosidic bond of not only pullulan but also amylopectin or derivative thereof. It produces maltotriose eventually from pullulan. The pullulanase, however, is known to produce a reverse synthetic action. By virtue of this action, this enzyme produces polymerized compounds such as a compound having six glucose units combined with one another, etc. from maltotriose, for example. When the pullulanase is additionally used in the saccharification of starch with glucoamylase, therefore, there is entailed a disadvantage that the saccharification gives rise to oligosaccharides of high molecular weights sparingly hydrolyzable with a glucoamylase owing to the reverse synthetic action inherent in the pullulanase, though the saccharification brings about a recognizable addition to the yield of glucose.